Air heating apparatus and control means therefor



Aug. 28, 1962 R. e. HICKS 3,051,161

AIR HEATING APPARATUS AND CONTROL MEANS THEREFOR Filed Sept. 16, 1957 jliiiiil'ii m 9 PIC-3.2

INVENT OR. ROBERT G. HICKS ATTORNEY United States Patent 3,051,161 AIR IEATING APPARATUS AND CONTROL MEANS THEREFOR Robert G. Hicks, Bettendorf, Iowa, assignor to American Air Filter Company, Inc., Louisville, Ky., a corporation of Delaware Filed Sept. 16, 1957, Ser. No. 684,100 3 Claims. (Cl. 126-110) This invention relates to air heater apparatus and more particularly to a fuel burner control system for air heater apparatus, the present invention comprising a modification of the invention set forth in assignees co-pending application Serial Number 600,347, filed July 26, 1956 by Aubrey H. Robson, now US. Patent No. 2,879,762.

As set forth in the abovementioned co-pending application, conventional oil burning air heaters include a heating cabinet containing an oil burner interconnected to a fuel supply by a manually operated valve, and a blower driven by an electric motor interconnected to a source of electrical energy by a manually operated switch, the blower creating a draft of air through the cabinet for heating purposes and supplying air under pressure to the burner for combustion purposes. To start this type of heater, the manually operated blower switch is first closed, the manually operated fuel oil valve is then opened to admit oil to the burner and the oil at the burner is then ignited.

As noted in the co-pending application, so long as the ignition of the fuel continues and the air in the cabinet does not reach a dangerously overheated temperature, the heater will operate satisfactorily. Recognizing that such conditions in an air heater might not be obtained under all conditions the co-pending application provides an air heater that automatically shuts itself down in proper sequence if the ignition of the fuel is discontinued for any reason or if the air temperature in the heater reaches a dangerously high value.

The present invention recognizes further that if there should be an insuflicient amount of air supplied to the combustion chamber due to an improper functioning of the blower through a sudden voltage drop or a blocking of the air ducts, an undesirable overheat condition or at least a smoking condition in the heater also can occur. To avoid the difficulties which could arise in such event, the present invention provides a fuel control circuit for an air heater which permits an automatic shutdown of the heater in proper sequence when the amount of combustion air supplied by the blower is insuliicient. The present invention further provides a fuel control circuit which permits the automatic running and shutdown of the heater in accordance with exhaust stack temperatures. With such an arrangement, it is possible to obtain prompt automatic operation when the burner flame is going and to stop fuel flow to the burner promptly in the event the flame should go out.

It is to be understood that various other features of the present invention will become obvious to one skilled in the art upon reading the disclosure set forth hereinafter.

More particularly, the present invention provides a control circuit for an air heater apparatus having a burner-containing combustion chamber, exhaust stack means for such combustion chamber, a fuel line for such burner, and blower means for supplying tempering air to be heated comprising; fuel flow control means disposed in such fuel line, a first electrical circuit connecting such blower means to a source of power, a second electrical circuit containing actuating means for such fuel flow control means connected to such source of power, first switching means common to both of the cirlCllllS including a manually closable normally openly biased switch member to complete the first circuit and energize the blower means and a temperature responsive switching member responsive to temperature in the exhaust stack means above a predetermined value to complete the first circuit independent of the manually closable switch member, and an air responsive switching means in the second electrical circuit responsive to a preselected rate of air delivery for the blower means to complete the second circuit to energize the fuel flow actuating means.

It is to be understood that various changes can be made in the arrangement, form and construction of the several parts of the apparatus disclosed herein without departing from the scope or spirit of this invention.

Referring to the drawings:

FIGURE 1 is a schematic vertical section of one advantageous embodiment of an air heater according to the present invention;

FIGURE 2 is a circuit diagram of an automatic electrical control system for the heater of FIGURE 1.

As can be seen in FIGURE 1 of the drawings, the air heater of the present invention comprises a cabinet 1 having an air inlet 2 positioned at the upper portion thereof and a warmed air outlet 3 positioned at the lower portion. Fastened to the upper portion above the air inlet 2 is a weather baflle and hood arrangement 4. A blower 5 for forcing air through cabinet 1 is positioned adjacent the air inlet 2 of the cabinet, the blower being driven by electric motor 6.

Positioned within cabinet 1 is a combustion chamber 7, the spaced walls of the combustion chamber 7 and the cabinet 1 forming a heat exchange area 8 therebetween. The combustion chamber 7 is provided in its upper portion with an air inlet opening 9 for admission of air for combustion purposes and an exhaust stack outlet means 11 which can be connected to a chimney (not shown) to carry the exhaust gases away. A bafiie 10 also is provided in the upper portion of the combustion chamber to insure a uniform distribution of exiting exhaust gases and to prevent such gases from short circuiting directly to the exhaust stack outlet means. Forming the lower portion of combustion chamber 7 is burner casing 12, the burner casing having supported therein perforated burner pot 13. The floor of burner pot 13 is provided with an opening 14 connected to inlet opening 9 of the combustion chamber by a preheat tube 15, a cone shaped flame spreader 16 being carried on the tube 15 above the burner pot. A hand port 20 is provided in cabinet 1, projecting through chamber 7 to permit insertion of a hand torch for ignition of the heater.

Connecting burner pot 13 to a fuel supply tank 18 is a fuel line 17. Included in this fuel line successively from the tank to the burner pot is a float valve mechanism 19 which maintains a constant pressure head for flow control, a metering orifice 21, a manual control valve 22, and a solenoid actuated shutoff valve 23. The opening or closing of shutoff valve 23 is dependent upon the operation of its solenoid in the circuit described hereinafter. It also will be seen in the circuit described hereinafter that to energize the solenoid of valve 23 after a flame is established in the burner pot 13 and thereafter identify proper conditions in which fuel can be permitted to flow to burner pot 13 through valve 23, a thermostatically operated switch member 24 is provided in the circuit. Switch member 24, which advantageously can be of the bi-metal actuated type, is positioned in the exhaust main 11 of the combustion chamber so as to be responsive to preselected exhaust stack temperatures at this exhaust main and thus insure prompt auto- '3 2 matic running and shut down of the heater at such preselected temperatures.

Positioned in warmed air outlet 3 is the overheat cutout switch 25, which switch is also included in the circuit described hereinafter. Switch 25 is a normally closed, thermally actuated, manually resettable safety switch and advantageously can be actuated by a conventional bi-metal actuator. When a prescribed overheat temperature occurs at outlet 3 the switch 25 is actuated .to an open position to break its circuit as described hereinafter. When the bi-metal has cooled to a lower temperature, the switch then can be reset manually.

To insure automatic shutdown of the heater in proper sequence in the event the amount of combustion air supplied to the heater should be insuihcient, an air flow responsive switch member 26 is provided, switch 26 being positioned above air inlet 2 to measure the mass flow rate of air as it enters cabinet 1. Although this switch member can be any one of various types, it advantageously is of the air velocity responsive type and includes a micro-switch portion 27 actuated by a sail member 28, the sail member 28 being secured tothe actuating lever of the micro-switch. The entire switch 26 is inserted in a rectangular box-like duct 29 having openings 31 in the front and back walls thereof. Duct 29 is positioned in the air stream which flows to air inlet 2 in such a manner that air flows through holes 31 and in so doing strikes sail 28. So long as the air velocity pressure is suflicient to move sail 28, the contact in microswitch portion 27 of switch 26 m'll stay closed.

As is obvious from FIGURE 1 of the drawings, cabinet 1 is secured in the total assembly by fastening the cabinet to a carriage 32.- In this connection, it will be noted that supply tank 18 is secured to carriage 32 by means of a support bracket 33, support bracket 33 also serving to support the aforedescn'bed fuel line system between tank 18 and burner pot 13.

Referring to FIGURE 2 of the drawings, it can be seen that the electrical control system for the air heater of FIGURE 1 is energized from a source of electrical energy supplied to terminals 34 and 35. The control system is arranged to provide across the terminals 34- and 35 a first electrical circuit 36, which circuit includes the motor 6 for blower 5, and a second electrical circuit 37 in parallel with the first electrical circuit 36.

Connected in the line determined by terminals 34 and 35 so as to be in common with parallel circuits 36- and 37 is blower motor control circuit 38. Circuit 38 includes -a motor starting, manually closable, normally openly biased switch member 39, which when closed serves to complete the first electrical circuit 38 to energize motor 6 of the blower. Circuit 38 further includes the aforedescribed temperature responsive, motor running switch member 24, which is positioned in exhaust stack means 11 (FIGURE '1) and which is responsive to close and open at preselected exhaust .gas temperatures. Switch 24 is arranged in parallel, or in shunt, with the manually closable switch member 39. Accordingly, when the temperature of the exiting gases at the exhaust stack means 11 rises above a certain preselected value, which can advantageously be 200 F., switch 24 closes to by-pass the manually closable, normally openly biased switch 39 and complete the electrical circuits 36 and 37, thus keeping blower motor 6 running. On the other hand, when the temperature in the exhaust stack means 11 falls below a second predetermined value, which advantageously can be 180 F., switch 24 opens to open circuit 36 and halt the operation of blower motor 6 and to open circuit 37. With such a temperature responsive switch 24 positioned in the exhaust stack means 11, it is thus possible to detect initially and promptly when a flamehas been established in the burner so that the manual closing of switch 39 can be discontinued. It is also possible to determine promptly when the flame has failed, as evidenced by a drop in temperature in the exhaust stack means 11. When this occurs, the solenoid 23 will be de-energized promptly, as is described hereinafter.

Connected in the second electrical circuit 3-7 is the air responsive switch member 26 (aforedescribed), this switch member, which is positioned above air inlet 2 and is responsive to the mass flow rate of air delivery to blower 5, serves to complete the circuit 37 when energized so as to permit energization of the fuel flow control solenoid valve 23 connected in a series with switch 26 in circuit 37. When solenoid valve 23 is energized, it opens fuel line :17 to permit the flow of fuel from supply tank 18 to burner pot 13. In the event air flow to blower 5 should drop below a preselected response value for switch 26, for such reasons as a sudden voltage drop or a blocking of the air ducts, switch 26 will open circuit 37 and solenoid valve 23 will be dc-energized to close and stop the flow of fuel to burner pot 413.

Also connected in the circuit 37, in series with solenoid valve 23 and switch 26 is the aforedescribed thermostatically controlled manually resettable overheat switch 25. Switch 25, which is positioned in warm air outlet 3, is set to open if the temperature of the air in the cabinet 1 should reach a dangerously high value, advantageously about 250 F.

In a typical operation of the above described apparatus, the manually resettable overheat switch 25 may be opened if the heater had previously shutdown because of an overheat condition. Leaving switch 25 open, the motor starting switch 39 is pushed for a short period (30 seconds) to energize the blower motor 6 and purge the heater of any excess fuel vapors, after which time, switch 39 is released and motor 6 is de-energized.

Switch 25 then is pushed to reset it in a closed position and valve 22 is manually opened. A lighted torch is inserted into the burner at hand port 20 and the motor starting switch 39 again is pushed to energize blower motor 6 to start a draft of air flowing through the cabinet 1. When the blower motor reaches the required speed to deliver sufiioient air for combustion and ventilation, the air flow switch 26 closes to complete circuit 37 and energize solenoid valve 23. Fuel then flows to burner pot 13 and a fire is established. The motor starting switch 39 is held down until the exhaust stack gases reach a preselected high temperature, advantageously 200 F. At this time, temperature responsive switch 24 closes and keeps motor 6 running.

Motor 6 continues to run normally unless the heater temperatures become too high and overheating results. If this occurs, overheat switch 25 opens (advantageously at 250 F.) to open circuit 37 and the solenoid valve 23 is de-energized, closing to shut-off the fuel supply to burner pot 13. Blower motor 6 continues to run until the exhaust stack temperature reaches a preselected low temperature, advantageously 180 F. A this time, switch 24 opens to also open circuits 38 and 36.

During normal operations, the unit can be stopped by turning off the manually controlled fuel valve 22. As explained above, the heater unit will continue to operate until the temperature falls to 180 F. at which time switch 24 opens to open circuits 35, 36 and 37.

From the above description of the operation, it can be seen that exhaust stack temperature responsive switch 24 serves as a flame out control and the air flow responsive switch 26 prevents overheating of the heater or a smoky condition thereof in the event of :a sudden voltage drop or a blocking of the heater air ducts.

The invention claimed is:

1. In air heating apparatus including a heating cabinet having disposed therein a burner-containing combustion chamber interconnected by :a fuel line to a source of fuel supply and having a motor driven blower means for supplying tempering air to said cabinet to be heated and combustion supporting air to the burner for combustion purposes, said combustion chamber having an exhaust stack means cooperating therewith, a control circuit comprising: fuel flow control means disposed in said fuel line, a first electrical circuit connecting said blowers means to a source of power, a second elec1rical circuit containing actuating means for said fuel flow control means connected to said source of power, first switching means common to both of said circuits including a normally openly biased switch member manually closable to complete said first circuit and energize said blower means and a temperature responsive switching means responsive to temperatures in said exhaust stack means above a predetermined value and after combustion is fully established to complete said first circuit independent of said manually closable switch member and air responsive switching means in said second electrical circuit responsive only to a preselected mass flow rate of air delivery by said blower means to complete said second circuit and energize said fuel flow control actuating means, said preselected mass flow rate of air being sufficient to obtain complete combustion of the fuel supplied to said combustion chamber.

2. In air heating apparatus including a heating cabinet having disposed therein a burner-containing combustion chamber interconnected by a fuel line to a source of fuel supply and having a motor driven blower means for supplying tempering air to said cabinet to be heated and combustion supporting air to the burner for combustion purposes, said combustion chamber having an exhaust stack means cooperating therewith, a control circuit comprising: fuel flow control means disposed in said fuel line, a [first electrical circuit connecting said blower means to a source of power, a second electrical circuit containing actuating means for said fuel flow control means connected to said source of power, first switching means common to both of said circuits including a normally openly biased switch member manually closable to complete said first circuit and energize said blower means and a temperature responsive switching means responsive to temperatures in said exhaust stack means above a predetermined value and after combustion is fully established to complete said first circuit independent of said manually closable switching means and second switching means disposed in said second electrical circuit for selectively controlling the energization of said fuel flow control actuating means after completion of said first electrical circuit, said second switching means being operable only when a preselected mass flow rate of air sufiicient to obtain complete combustion is being delivered by said blower means.

3. In air heating apparatus including a heating cabinet having disposed therein a burner-containing combustion chamber interconnected by a fuel line to a source of fuel supply and having motor driven blower means for supplying tempering air to said cabinet to be heated and combustion supporting air to the burner for combustion purposes, said heater cabinet having a common inlet for the tempering air and combustion supporting air and said combustion chamber having an exhaust stack means cooperating therewith, a control circuit comprising: fuel flow control means disposed in said fuel line, a first electrical circuit connecting said blower means to a source of power, a second electrical circuit connected to said source of power in parallel with a portion of said first electrical circuit, first switching means common to both of said circuits including a normally openly biased switch member manually closable to complete said first circuit and energize said blower means and r3. temperature responsive switching means responsive to temperatures in said exhaust stack means above a first predetermined value and after combustion is fully established to complete said first circuit independent of said manually closable switch member and responsive to temperatures in said exhaust stack means below a second predetermined value -to open said first circuit and halt the operation of said blower means and second switching means disposed in said second electrical circuit for selectively controlling the energization of said actuating means including air responsive switching means responsive only to a preselected mass flow rate of air delivery by said blower means through said common inlet to complete said second circuit and energize said fuel flow control actuating means, said preselected mass flow rate of air being sufficient to obtain complete combustion of the fuel supplied to said combustion chamber, and a manually closable temperature responsive switch member operative, after manual closure thereof, to open said circuit when the temperature of the tempering air reaches a third predetermined value at the high end of the operating range.

References Cited in the file of this patent UNITED STATES PATENTS 1,888,730 Madison Nov. 22, 1932 2,190,349 Beam Feb. 13, 1940 2,432,314 Holthouse Dec. 9, 1947 2,445,466 Arnhym July 20, 1948 2,569,877 Woodrufi Oct. 2, 1951 2,596,290 Ryder et al May 13, 1952 2,684,668 Culp et al. July 27, 1954 2,704,671 Reichelderfer Mar. 22, 1955 2,879,762 Robson Mar. 31, 1959 FOREIGN PATENTS 

